High speed solder deposition and reflow for a printed flexible electronic medium

ABSTRACT

The present disclosure related to a flexible electronic substrate assembly and a method and system of processing solder paste onto an electrical substrate. The assembly includes a flexible substrate having a solderable medium provided along the flexible substrate. A pattern of solder paste may be cured to a portion of the solderable medium. The solderable medium may be a generally continuous construction or a patterned construction relative to the flexible substrate. The substrate may be unwound from a roll of substrate material before solder paste is deposited thereon. The flexible electric substrate assembly may be formed though a roll to roll process. Infrared heat may be applied to the substrate with the solder paste deposit as the substrate is traveling along the process direction to reflow the solder paste as the substrate is traveling along the process direction at a high rate of speed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Utility application Ser. No.15/497,309 filed on Apr. 26, 2017 which claims priority to U.S.Provisional Application No. 62/327,681 filed on Apr. 26, 2016 and U.S.Provisional Application No. 62/434,111 filed on Dec. 14, 2016, each ofwhich is hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present disclosure relates to a system and method of depositingsolder paste along a flexible electronic substrate for use withelectronic devices. More specifically, the present disclosure relates toa printed flexible substrate construction along with a system and methodfor providing a deposition of a solder paste onto a substrate at a highrate of speed. The system, method and printed flexible substrate mayprovide a conductive, solderable medium able to provide a flexible,conductive bond for use in various products, including, for example,electronics, hybrid electronic connections and electronic devices.

BACKGROUND

Electronic devices have been assembled to be light-weight and compact.The operation, integration, and complication of chips in electronicdevices has increased over the years while the size of electronicdevices or components used are getting thinner and smaller, and thepitch of soldering spots is also being reduced. These developmentsexacerbate an existing problem of solder spattering that occurs insolder reflow processes such that spattered solder often leads toundesired bridging and contamination due to the shortening pitch ordistance between solders.

Generally, printed flexible electronics have been used in assembledelectronic devices. Known printed flexible electronics have long reliedon conductive adhesives such as solder and isotropic conductiveadhesives (ICA) to form connections between conductive components orconstructions. ICAs may be made with silver, copper, gold, or carbon andinclude a binder chemistry that includes epoxy, polyimide, or silicone,which are non-conductive. ICAs are typically utilized in processingbecause they include lower processing temperatures and higher printresolution. However, ICAs display performance limitations such as higherresistance, resistance gain with time, adhesion loss at hightemperatures, joint cracking due to thermal expansion coefficientmismatch, and moisture absorption. Additionally, ICAs may be applied toelectronic substrates and cured in a variety of mechanisms. Inparticular, ICAs may be snap cured, heat cured, room temperature cured,B-stage and two-component processed. These cure mechanisms may requirethat the electronic substrates to receive the ICA be in contact beforethe curing process.

Similarly, known solder reflow processes also may require that theelectronic substrates be in contact with the solder before the curingprocess. In a conventional solder reflow process, a substrate or carrieris first prepared to receive electrical components. Then, at least oneobject to be soldered is placed on the carrier in which the object ispositioned on the carrier through an application such as printing,dispensing, pick-and-place, plating, or other methods of application. Acomponent to be joined is positioned on the solderable object oralternatively, a component that carries at least a solderable object isplaced on the substrate. Afterwards, the substrate may be moved into ahigh-temperature reflow oven for carrying out a reflow process so as tohave the solderable object heated and melted to bond to the substrate.

The conventional reflow process may include a preheating zone, a soakingzone, a reflow zone, and a cooling zone, which may be utilized onsurfaces such as individual printed circuit boards or chips. Solderspattering may occur in different zones due to the use of differenttypes of solder. Further, the solder reflow process may take additionaltime to allow the solder paste to properly cure, as the current state ofthis technology requires a particular dwell time before substantialcuring may occur. In particular, current surface mount technology for aconventional reflow process may be relatively slow from the applicationto the curing time.

Disclosed are embodiments of an assembly, system, and method that mayassist with solving the problems that exist in the prior art. Thedisclosed assembly, system, and method may improve the processing speedrelated to applying solder to a substrate and improve the deficiencieswith ICAs for use in the electronics industry.

SUMMARY

The embodiments of the present disclosure described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

The present disclosure provides a method of processing solder paste ontoan electrical substrate. The method comprises depositing solder pasteonto an electronic substrate to form a solder paste deposit in apredetermined pattern as the substrate is traveling along a processdirection. Infrared heat may be applied to the substrate with the solderpaste deposit as the substrate is traveling along the process directionto reflow the solder paste. The solder paste may be dried withconvection heat as the substrate is traveling along the processdirection. The substrate may be cooled to cure the solder paste in thepredetermined pattern as the substrate is traveling along the processdirection.

In one embodiment, the infrared heat may be applied within a first zoneof an oven. The step of applying infrared heat to the substrate mayfurther comprise applying convective heat to the substrate with thesolder paste deposit. The solder paste may be dried in a second zone ofthe oven wherein the temperature within the second zone is independentlycontrolled from the temperature within the first zone of the oven. Thesubstrate may travel along the process direction at a speed that isgreater than about 30 fpm (9.14 mpm), at a speed that is greater thanabout 50 fpm (15.24 mpm), at a speed that is greater than about 75 fpm(22.86 mpm) up to about 100 fpm (30.48 mpm), at a speed that is greaterthan about 100 fpm up to about 300 fpm (91.44 mpm) and in particular aspeed that is greater than about 150 fpm (45.72 mpm) up to about 175 fpm(53.34 mpm). In particular, the substrate may travel along the processdirection at a speed between about 30 fpm and 100 fpm.

The present disclosure also includes a system for processing solderpaste onto an electrical substrate. The system comprises a solder pasteapplication station for applying solder paste to an electronic substrateto form a solder paste deposit in a predetermined pattern as thesubstrate is traveling along a process direction. An oven may beconfigured to apply infrared heat to the substrate with the solder pastedeposit as the substrate is traveling along the process direction toreflow the solder paste and to dry the solder paste with convection. Thesubstrate may be traveling along the process direction at a speed thatis greater than 30 fpm (9.14 mpm).

The oven may include a first zone and a second zone such that thetemperature within the first zone may be independently controlled fromthe temperature within the second zone. In embodiments of the disclosedsystem, the oven may be configured to run with any number of zones fromone to over 50 and generate favorable results. The oven may includeinfrared heaters to applied infrared heat within the first zone of anoven. The oven may apply infrared heat and convective heat to thesubstrate within the first zone. The solder paste may be dried in thesecond zone of the oven as convective heat is applied within the secondzone of the oven. The substrate may travel along the process directionat a speed that is greater than about 30 fpm (9.14 mpm), at a speed thatis greater than about 50 fpm (15.24 mpm), at a speed that is greaterthan about 75 fpm (22.86 mpm) up to about 100 fpm (30.48 mpm), at aspeed that is greater than about 100 fpm up to about 300 fpm (91.44 mpm)and in particular a speed that is greater than about 150 fpm (45.72 mpm)up to about 175 fpm (53.34 mpm).

The present disclosure is also related to a flexible electronicsubstrate assembly. The assembly includes a flexible substrate having asolderable medium provided along the flexible substrate. A pattern ofsolder paste may be cured to a portion of the solderable medium. Thesolderable medium may be a generally continuous construction relative tothe flexible substrate. Alternatively, the solderable medium may be apatterned construction relative to the flexible substrate. The substratemay be unwound from a roll of substrate material before solder paste isdeposited thereon. The flexible electric substrate assembly may beformed though a roll to roll process.

The solderable medium may include a thickness between about 0.05 microns(0.00197 mil) to about 3 microns (0.118 mil). Additionally, thesolderable medium may include a thickness between about 0.15 microns(0.0059 mil) to about 0.3 microns (0.0118 mil). The flexible substratemay include a thickness between about 0.5 mil (12.7 microns) to about 2mils (50.8 microns). Additionally, the flexible substrate may include athickness between about 0.8 mil (20.3 microns) to about 1.2 mil (30.5microns). The flexible electronic substrate assembly may include a totalthickness between about 0.5 mil (12.7 microns) to about 10 mils (254microns). Additionally, the flexible electronic substrate assembly mayinclude a total thickness between about 1.4 mils (35.6 microns) to about5 mils (127 microns). At least one printed trace may be provided alongthe surface of the flexible substrate. At least one secondary electricdevice may be attached to the solder paste along the solderable medium.

Other features and advantages of the present invention will becomeapparent to those skilled in the art from the following detaileddescription. It is to be understood, however, that the detaileddescription of the various embodiments and specific examples, whileindicating preferred and other embodiments of the present invention, aregiven by way of illustration and not limitation. Many changes andmodifications within the scope of the present invention may be madewithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

These, as well as other objects and advantages of this invention, willbe more completely understood and appreciated by referring to thefollowing more detailed description of the embodiments of the inventionin conjunction with the accompanying drawings, of which:

FIG. 1 illustrates a schematic cross sectional view of a solderablemedium with a patterned configuration along a substrate according to anembodiment of the present disclosure;

FIG. 2 illustrates a schematic cross sectional view of a solderablemedium with a continuous configuration along a substrate according to anembodiment of the present disclosure;

FIG. 3 shows a picture of solder paste positioned along an embodiment ofa substrate in accordance with an aspect of the present disclosure;

FIG. 4 shows a picture of solder paste position along an embodiment ofthe substrate in accordance with an aspect of the current disclosure.

FIG. 5 shows a picture of an embodiment of solder paste on a patternedsolderable medium positioned along a substrate;

FIG. 6 shows a picture of an embodiment of a patterned solderable mediumwith solder paste of the present disclosure;

FIG. 7 illustrates a schematic plan view of an embodiment of a patternedsolderable medium with solder paste and traces of the presentdisclosure;

FIG. 8 illustrates schematic plan views of embodiments of patternedapplied solder paste of the present disclosure;

FIG. 9 illustrates schematic plan views of additional embodiments ofpatterned applied solder paste of the present disclosure;

FIG. 10 illustrates a schematic plan view of an embodiment of apatterned solderable medium with solder paste and traces of the presentdisclosure;

FIG. 11A illustrates a front side of an embodiment of the electronicsubstrate assembly of the present disclosure;

FIG. 11B illustrates a back side of the electronic substrate assembly ofFIG. 11A.

FIG. 12 illustrates a schematic plan view of an operation according toan embodiment of the present disclosure;

FIG. 13 shows a picture of an embodiment of a solder paste applicationstation of the present disclosure;

FIG. 14 shows a picture of an embodiment of the solder paste applicationstation of the present disclosure;

FIG. 15 shows a picture of an embodiment of an infeed nip of the presentdisclosure;

FIG. 16 shows a picture of an embodiment of an infeed nip of the presentdisclosure;

FIG. 17 is a picture of an embodiment of an interior portion of a firstzone of an oven of the present disclosure;

FIG. 18 is a picture of an embodiment of an interior portion of a secondzone of an oven of the present disclosure;

FIG. 19 is a picture of a cooling portion of the oven of the presentdisclosure; and

FIG. 20 is a picture of an embodiment of an outfeed nip of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of thepresent teachings, examples of which are illustrated in the accompanyingdrawings. It is to be understood that other embodiments may be utilizedand structural and functional changes may be made without departing fromthe respective scope of the present teachings. Moreover, features of thevarious embodiments may be combined or altered without departing fromthe scope of the present teachings. As such, the following descriptionis presented by way of illustration only and should not limit in any waythe various alternatives and modifications that may be made to theillustrated embodiments and still be within the spirit and scope of thepresent teachings.

The assemblies and methods disclosed in this document are described indetail by way of examples and with reference to the figures. Unlessotherwise specified, like numbers in the figures indicate references tothe same, similar, or corresponding elements throughout the figures. Itwill be appreciated that modifications to disclosed and describedexamples, arrangements, configurations, components, elements,apparatuses, methods, materials, etc. can be made and may be desired fora specific application. In this disclosure, any identification ofspecific shapes, materials, techniques, arrangements, etc., are eitherrelated to a specific example presented or are merely a generaldescription of such a shape, material, technique, arrangement, etc.Identifications of specific details or examples are not intended to be,and should not be, construed as mandatory or limiting unlessspecifically designated as such. Selected examples of assemblies andmethods are hereinafter disclosed and described in detail with referencemade to the Figures.

As illustrated by FIGS. 1 and 2, the present disclosure relates to aflexible electronic substrate assembly 10 of either a continuous or apatterned deposit of a solderable medium 20, 22 on a flexible substrate30. FIG. 1 illustrates the assembly 10 with a patterned solderablemedium 20 and FIG. 2 illustrates the assembly with a continuoussolderable medium 22. The flexible electronic substrate assembly 10 maybe adapted to be used with a continuous roll to roll based process forsurface mounting technology (SMT) in the electronics industry. A roll toroll based process may allow the substrate to receive various layers asthe substrate travels along a process direction at a high rate of speed.The disclosure includes applying or dispensing solder paste onto thesubstrate. Further, the substrate may also include various arrangementsof electronic traces such as a layer of conductive ink. The system andmethod allow for depositing solder paste onto the moving substrate at ahigh rate of speed and with improved accuracy relative to other knownmethods and systems.

The solderable medium 20, 22 may be a conductive material such as ametal foil that may be formed utilizing an additive technique such asvapor deposition, sputtering or use of a nucleating agent in a patternto which material is subsequently applied. Additionally, the solderablemedium 20, 22 may be formed by a subtractive technique such as etching,cold foil, or hot stamping. Some examples of materials that may be usesas the solderable medium 20, 22 include silver, copper, tin, and nickel.However, other materials, metals, or alloys may be used and thisdisclosure is not limited in this regard. The solderable medium 20, 22may include one or more layers of one or more conductive metals. Thesolderable medium 20, 22 may include a thickness that ranges betweenabout 0.05 microns (0.002 mil) to about 3.0 microns (0.118 mil) and mayfurther range between about 0.15 microns (0.006 mil) to about 0.3microns (0.012 mil). Additionally, the solderable medium 20, 22, may bea printed conductive material wherein such material may include silver,copper, silver and copper, or silver coated copper. The solderablemedium 20, 22 as a printed conductive material may include one or morelayers of one or more conductive materials and may include a thicknessthat ranges between about 0.5 mil (12.7 microns) to about 2 mils (50.8microns) and may further range between about 0.8 mil (20.3 microns) toabout 1.2 mils (30.5 microns).

The flexible substrate 30 may be a polymeric film. In particular, thepolymeric film may include polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyimide (PI), or other polymer basedmaterials such as polyethylene (PE), polypropylene (PP) and polyvinylchloride (PVC). The flexible substrate 30 may be flexible to allow it tobe processed in a roll to roll operation. The flexible substrate 30 mayinclude a thickness that ranges between about 0.5 mil to about 10 milsand may further range between about 1.4 mils to about 5 mils. Theflexible substrate 30 may include a treatment such as a surfacetreatment to assist with ink or metal adhesion. This treatment mayimprove the adhesion to the solderable medium 20, 22. The flexiblesubstrate 30 may include a characteristic that allows it to bedimensionally stable through a range of temperatures and in particulardimensionally stable at high temperatures, such as temperatures inexcess of 150° C. The flexible substrate 30 may undergo a treatment orprocessing step to provide heat stabilization.

In one embodiment, the flexible substrate 30 may include a thickness ofabout 0.2 micron (0.008 mil) up to about 100 microns (4 mils). In oneembodiment, the thickness of the substrate was between about 10 to 90microns (0.4 mil to 3.5 mils) and more particular about 75 microns (3.0mils). Additionally, various ranges of substrates thicknesses have beenevaluated including substrates that may include a layer of conductiveink 22. This ink may be applied to the substrate prior to the solderpaste and before being processed through an oven. This ink 22 may have athickness between about 0.5 mil (12.7 microns) to about 1.5 mils (38.1microns) and more particularly about 0.8 mil (20.3 microns) to about 1.2mils (30.5 microns). The thickness identified represent the conductiveink thickness in a dried state without the substrate. This type ofconductive ink may be solderable and may contain silver, silver coatedcopper, or silver and copper. The ink may be applied to a substrate(such as PET) prior to the solder paste 40 (and the oven). Thissolderable ink may be alternatively used to metalized copper or othertypes of electrical traces provided on the substrate.

The solder paste 40 may be applied to the solderable medium 20, 22 toprovide a robust conductive bond between conductive materials. Thesolder paste 40 may be deposited in a variety of configurations anddimensions which may be defined by the application requirement. Thesolder paste 40 may be a “No Clean” type wherein the application of thesolder paste 40 to the solderable medium 20, 22 may not include the useof solvents to remove residue. The solder paste 40 may include metalconstituents which may be selected based on the conductive materials tobe bonded and other material processing limitations. Solder paste 40 mayinclude two or more materials such as tin, bismuth, silver, indium, orzinc. The solder paste 40 may have a reflow temperature that is lessthan 200° C. and preferable less than 165° C. In one embodiment, theamount of flux contained in the solder paste 40 may be minimized such asless than 20% by weight. Further, the solder paste may include fastdrying solvents or resins. The thickness and dimensions of the solderpaste 40 may be defined by the application and process requirements orlimitations. Although these features of the solder paste 40 may describean embodiment of the instant disclosure, it is understood that varioustypes of solder paste 40 may be utilized made of different materials orconfigurations and this disclosure is not limited in this regard.

FIGS. 3-6 illustrate various embodiments of the flexible electronicsubstrate assembly 10. FIG. 3 shows a picture of an embodiment of theflexible electronic substrate assembly 10 having a plurality of solderpaste elements 40 positioned along the continuous solderable medium 22as it is positioned along the flexible substrate 30. FIG. 4 shows apicture of flexible electronic substrate assembly 10 having a pluralityof solder paste elements 40 position along a first patterned solderablemedium 20 as it is positioned along a second patterned solderable medium20 as both are positioned along the flexible substrate 30. FIG. 5 showsa picture of an embodiment of solder paste 40 on a patterned solderablemedium 20 positioned along a substrate 30. FIG. 6 shows a picture of anembodiment of the patterned solderable medium 20 with solder paste 40which was die cut from the flexible substrate of FIG. 4.

Similarly, FIG. 7 illustrates an embodiment of solderable medium 20 thathas been die cut into a particular shape that includes solder paste 40on edges of the patterned solder medium 20. The solder paste 40 may bein communication with printed traces 50 that extend from the solderpaste 40 to solder paste 40 along opposite edges thereon. The flexibleelectronic substrate assembly 10 may be combined with other electronicdevices to allow electronic communication from solder paste 40 throughprinted traces 50 to solder paste 40. The solder paste 40 and printedtraces 50 may incorporate a variety of configurations along the flexibleelectronic substrate assembly 10 that allow for the assembly to beprocessed from roll to roll. The printed traces 50 may include a varietyof patterns and arrangements.

As illustrated by FIGS. 8, and 9, provided are various embodiments ofthe flexible electronic substrate assembly 10. In each embodiment,flexible substrates 30 are illustrated in a roll to roll processingconfiguration. Wherein the solder paste 40 may be applied in variousgeometries including but not limited to circles, squares, rectangles,lines. Further, the solder paste can be applied in a series ofcontinuous bands or a plurality of segmented bands positioned on theconductive substrate to match the application required positions. Thelength and width of the bands or segmented bands may be determined bythe engineering requirements of the application. Typically, thedimensions of the bands and segmented based would be limited to just thepositions requiring conductive bonding given the tolerances of thejoining process throughout the continuous roll. This allows the rollwith the solder and solderable conductive areas to be wound into aconvenient form for subsequent processing. Such a roll can be utilizedas a component part to obviate the need to apply solder in a lateroperation. Such a roll format can be laminated to support structures orused in a flexible form factor as required. The roll can be subsequentlysheeted into individual units of use in subsequent processing.

As illustrated by FIG. 10, a secondary electronic device 60 may beadhered to the solder paste 40 before the reflow process. The secondaryelectronic device 60 may be any electronic element desired tocommunicate electronically with another electronic device 60 through theflexible electronic substrate assembly 10. This configuration may resultin a robust conductive bond. The resultant product may likely requiredie cutting or sheeting for storage or handling purposes. In oneembodiment, the secondary device may be applied in separate processingstep. In this case, the substrate 30 and the solderable medium 20, 22with solder paste 40 may be wound into a roll for storage or shipmentprior to being combined with the secondary device 60. The created rollcould be processed further to customize the product for an application.A subsequent bond may be created during a second reflow process. Thesecond reflow process would preferably include a fluxing step of thesecondary device 60 to the electronic substrate assembly 10.Additionally, a secondary or tertiary device may be a battery such as acoin cell wherein the secondary device is not soldered to the substrateassembly 10 but electrical traces are configured to electricallycommunicate with the battery.

FIG. 11A illustrates a front side of an embodiment of the electronicsubstrate assembly and FIG. 11B illustrates a back side. This embodimentof the substrate assembly 10 utilizes additional processing steps toconfigure the electronic substrate assembly 10 as desired. For example,additional layers of solder paste 40 or printed traces 50 may be printedor deposited on the substrate 10. Additionally, more than one type ofconductive material or inks (such as both silver and carbon type inks)may be applied in various patterns on substrate assembly 10 wherein atleast one the conductive materials may be solderable. The substrateassembly may include various die cuts, punches, vias, or slots toarrange the assembly as desired for the final application. Asillustrated by FIG. 11B, conductive materials may also be applied alongthe back side of the substrate assembly 10 in various configurations.This material may or may not be in electrical communication with thefront side.

These configurations may be utilized in a variety of electricapplications that include printed flexible electronics and flex-rigidelectronics. In one embodiment, the electronic substrate assembly 10 maybe utilized for making permanent contact between a printed battery and aprinted circuit in a sensor. In another embodiment, the electronicsubstrate assembly 10 may be utilized to provide electrical connectionsbetween rigid subassemblies that may replace wiring harnesses inautomotive applications.

In particular, known surface mounting technology (SMT) in theelectronics industry is only capable of operating at less than about 30feet per minute (fpm) or about 9 meters per minute (mpm). However, theassembly and method of the instant disclosure is capable of operating ata rate of speed higher than 30 fpm (about 9 mpm). In embodiments, thepresent system and method provide for depositing solder at a rate ofspeed of about 50 fpm (about 15 mpm) or greater; about 60 fpm (about 18mpm) or greater; about 75 fpm (about 23 mpm) or greater; even about 85fpm (about 26 mpm) or greater. In embodiments, the system and methodallow for operation at speeds from about 50 fpm (about 15 mpm) to about100 fpm (about 30 mpm) from about 60 fpm (about 18 mpm) to about 90 fpm(about 27 mpm); even from about 60 fpm (about 18 mpm) to about 80 fpm(about 24 mpm). In one embodiment, the system and method can operate atspeeds from about 75 fpm (about 23 mpm) to about 100 fpm (about 30 mpm).Further, the system and method may operate at speeds from 100 fpm (about30 mpm) up to about 300 fpm (about 91 mpm) and in particular it mayoperate at speeds that are greater than about 150 fpm (about 46 mpm) upto about 175 fpm (about 53 mpm).

FIG. 12 illustrates a schematic view of a system 100. In particular, asubstrate material 110 may be introduced at an unwinding station 120.The substrate 110 may be made of a thin metalized material such ascopper. The substrate 110 may have various metal traces or contactsthereon and be made of various metal materials or alloys and thisdisclosure is not limited to any particular materials or substrates.

Additionally, in one embodiment, a substrate 110 may be a foil havingthicknesses between about 0.15 micron (0.006 mil) to about 0.30 micron(0.012 mil). However, this disclosure is not limited to the thickness orthis particular type of the substrate as various configurations may beutilized without damaging or distorting the substrate 110 or assembly.

The substrate 110 may generally be a continuous substrate material andmay initially be provided in roll form. The substrate 110 may be unwoundat the unwinding station 120 to travel along a process direction D to asolder paste application station 130. In one embodiment, the solderpaste application station 130 may include a dispensing valve 132 asillustrated by FIG. 13. Additionally, it may include a rotary screen 134as illustrated by FIG. 14. The solder paste application station 130 mayapply a solder paste 140 to the substrate 110 at predetermined patternsthat may be in electric communication with various trace featurespresent in or on the substrate 110. Additionally, solder paste 140 maybe applied to the substrate at the station 130 via stencil, continuousflat bed screen assembly, or a screen print including a rotary screenand a squeegee. The solder paste 140 may be delivered to the substrate110 by operation of a pump such as a pneumatic displacement pump or thelike.

The substrate 110 may then be processed through to the oven 160 toreflow the solder paste and reduce the cure time of the solder paste 140on the substrate 110. The substrate 110 may extend over an infeed nip150 before entering the oven 160. The infeed nip 150 may assist toisolate tension to the substrate 110 as it extends through the oven 160to an outfeed nip 170 along the process direction D. The substrate 110may subsequently be rewound at a rewind station 180 after the solderpaste 140 has been cured thereon.

The infeed and outfeed nips 150, 170 may allow the substrate 110 to movewithin the oven 160 while maintaining tension forces thereon. Thetension forces allow the substrate 110 to travel though the oven 160without sagging, distortion or otherwise causing damage to the substrate110 as it moves therethrough at high rates of processing speeds. FIGS.15 and 16 illustrate various embodiments of the infeed nip 150 of thepresent disclosure. In one embodiment, the substrate 110 may beprocessed in a segmented orientation as arranged along its width. FIG.17 illustrates an embodiment of the outfeed nip 170.

As illustrated by FIG. 12, the oven 160 may include a first zone Z1 anda second zone Z2 wherein the first and second zones maintain independenttemperature control relative to the other. This disclosure is notlimited to the number of zones provided. Further, a third zone Z3 may bepositioned after the second zone Z2. The first zone Z1, second zone Z2,and third zone Z3 may be configured to allow for independent airvelocity and control therein. The first zone Z1 may be able to deliverhigh heat to reflow the solder paste 140 within a particular time suchas within five (5) seconds as the substrate 110 travels along theprocess direction D. The particular heat applied through the first zoneZ1 may include at least one of convection heat and radiant heat whereinthe radiant heat may be applied by near, short, or mid wave infraredheaters. Alternatively, electron beam energy may also be used to deliverhigh heat to reflow the solder paste in lieu of or in addition to, theinferred heaters. In embodiments of the disclosed system, the oven 160may be configured with any number of zones from one to over 50 that areconfigured to generate favorable results and this disclosure is nonlimiting in this regard.

FIGS. 17 and 18 illustrate interior portions of the first zone Z1 andsecond zone Z2 of the oven 160, respectively. Notably, the oven 160 mayinclude air impingement nozzles 162 within the first and second zonesZ1, Z2. The impingement nozzles 162 may extend from a top surface and abottom surface relative to the substrate 110 therein and may includediffusers 164. The diffusers 154 may be removeable and configurablebased on the particular type of desired pattern of airflow. Theimpingement nozzles 162 may assist to control convective heat airflowagainst the substrate 110 and the solder paste deposited thereon. Thenozzles may provide hot air between 340° F. (171° C.) to about 375° F.(191° C.) or up to about 400° F. (204° C.). Further, the oven 160 mayinclude heaters 166 at various locations to provide energy to thesubstrate. In one embodiment, the heaters are infrared heaters 166 thatprovide infrared heat energy to the substrate. In another embodiment,the heaters 166 may be an electron beam type heaters. Additionally,other types of energy sources may be utilized herein that are sufficientto reflow the solder.

The heaters 166 may be located between impingement nozzles 162 withinthe first zone Z1 of the oven 160. The infrared heaters 166 may be dualbulb type to provide short wavelength type IR energy. The infraredheaters 166 may be configured to provide heat between about 1600° F.(871° C.) to 3000° F. (1949° C.) and more particularly could provide upto about 4000° F. (2204° C.). For example, infrared heaters 166 couldprovide short wavelength type IR energy between about 1292° F. (700° C.)to 3272° F. (1800° C.) while infrared heaters 166 operating in the nearinfrared condition may provide be configured to provide heat betweenabout 3272° F. (1800° C.) to 6512° F. (3600° C.). There may be infraredheaters provided along a six (6) foot portion along the processdirection D and adjacent the initial entrance of the oven 160 at thefirst zone Z1.

In one embodiment, the infrared heaters 166 may provide energy along aparticular length of the substrate 110 (such as 24″ or 0.61 m) as it ispositioned within the oven 160. In particular, the infrared heaters 166may be positioned along an entrance of the oven 160 wherein various IRheaters may be provided as needed adjacent the opening of the oven 160.The size and amount of the IR heaters 166 may be provided based on thedesired processing speeds of the substrate 110 as it is passed throughthe oven 160 and exposed to the particular lengths of energy emittedfrom the IR heaters 166. For example, one IR heater 166 may emit energyalong 24″ (0.61 m) length of the substrate. If the substrate 110 isbeing processed along the process direction D at various speeds, thesolder paste thereon may be exposed to the emitted IR energy for varioustimes. For speeds of 50 feet per minute (fpm) (15.24 meters perminute—mpm), for example, the substrate 110 may be exposed to a 24″ ofemitted IR energy from the IR heater 166 for about 2.4 seconds. Forspeeds of 75 fpm (22.86 mpm), the substrate 110 may be exposed to a 24″of emitted IR energy from the IR heater 166 for about 1.6 seconds. Forspeeds of 100 fpm (30.48 mpm), the substrate 110 may be exposed to a 24″of emitted IR energy from the IR heater 166 for about 1.2 seconds. Forspeeds of 150 fpm (45.72 mpm), the substrate 110 may be exposed to a 24″of emitted IR energy from the IR heater 166 for about 0.8 seconds. Forspeeds of 175 fpm (53.34 mpm), the substrate 110 may be exposed to a 24″of emitted IR energy from the IR heater 166 for about 0.7 seconds. Forspeeds of 300 fpm (91.44 mpm), the substrate 110 may be exposed to a 24″of emitted IR energy from the IR heater 166 for about 0.4 seconds.However, additional IR heaters 166 may be provided as desired toincrease the length of emitted energy exposure along the substrate 110.

Additionally, various process rolls may be provided within the oven toassist with supporting the structural integrity of the substrate 110 asit is translating through the oven 160. In one embodiment, the IRheaters may not be necessary for process speeds below 100 fpm.Additionally, this system may also incorporate various energy sourcessuch as electron beam devices and laser devices in place of the IRheaters. These energy sources may be helpful for reflowing solder atspeeds in excess of 100 fpm.

After being exposed to the first zone Z1 of the oven 160, the solderpaste 140 on the substrate 110 may activate the solder flux that mayinclude solvents and have a generally tacky configuration. After passingthrough the second zone Z2 of the oven 160, the substrate may enter aconvection cooling portion 172. As illustrated by FIG. 19, convectivecooling portion 172 may be in a third zone Z3 wherein convective coolingmay be provided to the substrate 110 during processing after exiting thefirst zone Z1 and the second zone Z2. The convective cooling portion 172may alternately be provided in the second zone Z2 if no additional zonesare present. The convective cooling portion 172 may be provided along anexit portion of the oven 160 wherein convective heat is provided at aparticular temperature and traversed over the substrate 110. Here, anyextraneous solvents may be removed from the solder flux wherein theconvective cooling portion 172 may further cool or dry the substrate 110and solder paste 140 as it exists thereon. Upon exiting the oven 160,the solder paste 140 may be dry and non tacky, and the substrate is incondition to be rewound at the rewinding station 180 withoutinterrupting the solder paste configuration.

Additionally, the substrate 110 may also be processed over a conductivecooling portion 174 after the convective cooling portion 172. In oneembodiment, the conductive cooling portion 174 may be a chill drumprovided along the process direction D of the substrate 110 as it exitsthe oven 160 before being rewound. Notably, tension of the substrate 110may be adjusted or isolated between the infeed and outfeed nips 150, 170or from other independent segmented nips that may be provided along theprocess direction D.

The formulation of the solder paste 140 may be adjusted to accommodatethe shear stress generated by the relatively high processing speeds ofthe process 100. The specific formulation of the solder paste may bedependent on the deposition method. FIGS. 3 and 4 illustrate variousembodiments of the solder paste 40 as it is dispensed and cured alongthe substrate 10 in a predetermined pattern. As illustrated by FIG. 4,the solder paste 40 may be cured in a pattern that overlaps variouselectrical traces or conductors on the substrate 10.

Accurately dispensing solder paste in predetermined patterns andproviding solder reflow at higher process speeds may be achieved throughthe use of infrared and/or near infrared heat in combination withconvection heat. After exposure to the infrared and/or near infrared,the solder paste converts to a flux that may remain tacky due to theminimal dwell times associated with the process. However, the tackynature of the flux is undesirable as the substrate 110 may be intendedto be processed in roll form. Convection heating may also be provided toassist with reducing the tacky nature of the solder paste flux.Additionally, the solder paste may be treated with various solvents toassist with the drying rate thereof.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it will be apparent to those of ordinary skill in the art that theinvention is not to be limited to the disclosed embodiment, and thatmany modifications and equivalent arrangements may be made thereofwithin the scope of the invention, which scope is to be accorded thebroadest interpretation of the appended claims so as to encompass allequivalent structures and products.

Although the embodiments of the present teachings have been illustratedin the accompanying drawings and described in the foregoing detaileddescription, it is to be understood that the present teachings are notto be limited to just the embodiments disclosed, but that the presentteachings described herein are capable of numerous rearrangements,modifications and substitutions without departing from the scope of theclaims hereafter. The claims as follows are intended to include allmodifications and alterations insofar as they come within the scope ofthe claims or the equivalent thereof.

The invention claimed is:
 1. A flexible electronic substrate assemblycomprising: a flexible substrate; a solderable medium provided along theflexible substrate, wherein the solderable medium is at least one of agenerally continuous construction and a patterned construction relativeto the flexible substrate; a pattern of solder paste cured to a portionof the solderable medium; and wherein the solderable medium includes athickness between about 0.05 microns to about 3 microns.
 2. The flexibleelectronic substrate assembly of claim 1, wherein the substrate isunwound from a roll of substrate material before solder paste isdeposited thereon.
 3. The flexible electronic substrate assembly ofclaim 1, wherein flexible electric substrate assembly is formed though aroll to roll process.
 4. The flexible electronic substrate assembly ofclaim 1, wherein the solderable medium includes a thickness betweenabout 0.15 microns to about 0.3 microns.
 5. The flexible electronicsubstrate assembly of claim 1, wherein the flexible substrate includes athickness between about 12.7 microns to about 50.8 microns.
 6. Theflexible electronic substrate assembly of claim 5, wherein the flexiblesubstrate includes a thickness between about 20.3 microns to about 30.5microns.
 7. The flexible electronic substrate assembly of claim 1,wherein the flexible electronic substrate assembly includes a totalthickness between about 0.5 mil to about 10 mils.
 8. The flexibleelectronic substrate assembly of claim 7, wherein the flexibleelectronic substrate assembly includes a total thickness between about1.4 mils to about 5 mils.
 9. The flexible electronic substrate assemblyof claim 1 further comprising at least one printed trace on the flexiblesubstrate.
 10. The flexible electronic substrate assembly of claim 1,wherein the substrate assembly is an electric device that is attachableto one or more devices wherein at least one secondary electric device isattached to the solder paste along the solderable medium.
 11. A flexibleelectronic substrate assembly comprising: a flexible substrate thatincludes a thickness between about 12.7 microns to about 50.8 microns; asolderable medium provided along the flexible substrate, the solderablemedium includes a thickness between about 0.05 microns to about 3microns; a pattern of solder paste cured to a portion of the solderablemedium, wherein the substrate assembly is an electric device that isattachable to one or more devices; and wherein the solderable medium isat least one of a generally continuous construction and a patternedconstruction relative to the flexible substrate.
 12. The flexibleelectronic substrate assembly of claim 11 further comprising at leastone secondary electric device attached to the solder paste along thesolderable medium.
 13. The flexible electronic substrate assembly ofclaim 11, wherein the flexible electronic substrate assembly includes atotal thickness between about 0.5 mil to about 10 mils.
 14. The flexibleelectronic substrate assembly of claim 11, wherein the substrate isunwound from a roll of substrate material before solder paste isdeposited thereon.
 15. The flexible electronic substrate assembly ofclaim 11, wherein flexible electric substrate assembly is formed thougha roll to roll process.